As a semiconductor device, a power semiconductor module has been known in which one or more power semiconductor elements (semiconductor chips) are provided in a case and the case is sealed with a sealing material. In the power semiconductor module used in, for example, an inverter circuit, a switching element, such as an insulated gate bipolar transistor (IGBT) or a metal oxide semiconductor field effect transistor (MOSFET) and a passive element, such as a free wheeling diode (FWD) are used as the semiconductor elements. The power semiconductor elements are mounted as semiconductor chips made of silicon or silicon carbide (SiC) on an insulating substrate and are electrically connected to electrical circuits or terminals formed on the insulating substrate. For example, an electrode formed on the upper surface of the semiconductor chip of the power semiconductor module is electrically connected to the electrical circuit or the terminal formed on the insulating substrate by an aluminum bonding wire or a copper lead (conductive plate). The bonding wire or the lead has a function of transferring heat generated from the semiconductor chip, in addition to the electrical connection function.
In recent years, the power semiconductor module is used under a higher capacity condition than the related art or is used in a high temperature environment such as an in-vehicle environment. In addition, with a reduction in the size of the semiconductor chip and an increase in the density of the semiconductor chips in the case, the heating temperature of the semiconductor chip is likely to increase.
One of measures for improving the dissipation of heat generated from the semiconductor chip to suppress an increase in the heating temperature of the semiconductor chip is to increase the number of aluminum bonding wires which are bonded to the electrodes formed on the upper surface of the semiconductor chip. However, with a reduction in the size of the semiconductor chip, it is difficult to bond a large number of bonding wires to the upper surface of the semiconductor chip.
In a semiconductor device in which a copper lead (conductive plate) is soldered to the electrode formed on the upper surface of the semiconductor chip, the lead can be bonded to the upper surface of the semiconductor chip by solder in a wide range. Therefore, this type of semiconductor device has a higher radiation performance than the structure in which the bonding wire is bonded. However, when the semiconductor chip and the lead are bonded by solder, long-term reliability is reduced since the difference between the thermal expansion coefficient of the semiconductor chip and the thermal expansion coefficient of the lead is large. Therefore, it is necessary to improve the long-term reliability.
A semiconductor device with high reliability has been proposed in which a semiconductor chip and a printed circuit board that is provided above the semiconductor chip are connected by a plurality of post electrodes and the plurality of post electrodes is connected to the semiconductor chip (Patent Document 1). However, in the semiconductor device disclosed in Patent Document 1, since the printed circuit board is connected to the semiconductor chip through the post electrodes, it is difficult for a large amount of current to flow to the printed circuit board and costs are higher than that in the structure in which the lead is used. In addition, the position of the post electrode is determined by the position of a through hole provided in the printed circuit board. Therefore, flexibility in the arrangement of the semiconductor chip in the power semiconductor module is not high.
A semiconductor device has been proposed in which a heat spreader is bonded to an electrode of a semiconductor chip and the heat spreader and a lead are bonded to each other by laser welding (Patent Document 2). The heat spreader used in the semiconductor device disclosed in Patent Document 2 is generally a simple copper plate and there is a difference between the thermal expansion coefficient of the heat spreader and the thermal expansion coefficient of the semiconductor chip. Therefore, it is necessary to improve reliability for a temperature cycle when a power semiconductor module is used.